Mercury resistance is among the most widely found resistance characteristics of the naturally-occurring plasmids of bacteria and is found on the same plasmids which carry resistance to antibiotics in many diverse genera. Mercury resistant bacteria can easily be found in urban sewage and are particularly numerous in water exposed to industrial pollution. We are working on a molecular level understanding of mercury resistance in bacteria by employing both conventional genetics and recombinant DNA technology. We have established that synthesis of the nercuric ion reductase enzyme (which we had described previously) is responsive to the level of glucose in the growth medium and is markedly enhanced by cAMP. The reductase enzyme is one of four polypeptides whose synthesis can be detected in plasmid-carrying minicells induced with mercuric chloride. The other polypeptides are all of low molecular weight and may be related to the transport of mercuric ion into the cell. Our genetic data suggests that the reductase may play a role in the regulation of its own systhesis and that of other polypeptides of the operon. We plan to continue characterization of the polypeptides produced in the minicell system by mutants in the mer operon; to generate additional mutants in bacteriophage lambda specialized transducing phages carrying the mer operon; to examine the nature of regulation in this system by employing fusions of the mer operon regulatory elements to the easily assayable enzyme, beta-galactosidase and to complete a fine structure restriction map of the operon and thereby place the "promoter" segment which we have cloned from the operon. All of the above studies have been carried out using the gene from a plasmid of E. coli. Once we have achieved an adequate understanding of the operation of this prototype system, we plan to extend these studies to examples of the mercury resistance system in other bacteria. At present, it appears that these systems are very similar, biochemically, to that of E. coli. Future work should provide comparisons of the evolution of regulatory and transport mechanisms in these procaryote detoxification systems.